The type II alveolar epithelial cell has critical biological roles: it is the source of pulmonary surfactant, and it also serves as a stem cell for the alveolar lining. Type II pheumocytes from nonhuman sources have been much studied recently, but for the purposes of human clinical application, such studies are only relevant to the extent they reflect properties of the human lung. This proposal is to isolate type II pneumocytes from human lung and characterize some of their metabolic, immunologic and ultrastructural properties. Type II pneumocytes will be isolated from autopsy material of both adults and premature infants and from lung tissue obtained from adult organ donors. Cells freshly isolated will be studied as to their surfactant phospholipid and protein composition, their quantity of enzymes for surfactant synthesis, their substrate preference and utilization, and their secretory properties. Further studies of human type II pneumocytes will define some of their surface antigens, and monoclonal antibodies will be generated to them. A major focus of studies will be factors that influence the ability to maintain differentiated features of type II pneumocytes in cell culture. Study of material obtained from premature infants, some of whom will have been treated with exogenous surfactant, may increase our understanding of the Respiratory Distress Syndrome of the newborn and its potential treatment. These studies will help determine the relevance of previous research on type II pneumocytes from nonhuman sources and should provide new information regarding the unique properties of human type II pneumoctyes.